Hydraulic system



Oct. 8, 1963 K. E.- MOAFEE, JR., ETAL 3,106,135

HYDRAULIC SYSTEM 3 Sheets-Sheet 1 INVENTOR KYLE E. M AFEE ,JR. CHARLES A.L.RUHL.

Filed July 15. 1961 BY 909 We 0% ATTORNEYS} Oct. 8, 1963 K. E. MOAFEE, JR.. ETAL 3,106,135

HYDRAULIC SYSTEM 7 Filed July 13, 1961 3 Sheets-Sheet 2 mm a 1mm 1 I 02: I k\ l /V 1 '57 {k 62 69 53 1\ 1\ m I&& my

76 5 6| I ,n 1 I 77 6745 56:1.565 INVENTOR KYLE EM AFEE CHARLES ALRUHL ATTORNEY Filed July 1-3, 1961 K. E. MOAFEE, JR., ETAL 3,106,135

ATTORNEY United States Patent 3,106,135 HYDRAUHC SYSTEM Kyle E. McAfee, Jan, and Eharles A. L. Ruhl, both of Kalamazoo, Mich, assignors to The New York Air Brake Company, a corporation of New'Jersey Filed iuiy 13, 1961, Ser. No. 123,772 8 (Ilairns. (Cl. 91-217) This invention relates to a remote control system for positioning the movable element of a hollow-plunger fourposition directional control valve.

The use of hollow-plunger four-position directional control valves in the hydraulic systems of heavy duty machinery and equipment is well known. Such valves normally include a housing having an inlet port connected with a source of high pressure fluid, an outlet port connected with a sump, and a pair of motor ports connected, respectively, with the connections of a hydraulic motor which is to be operated. A valve plunger is movable in the housing between a neutral position in which the inlet port is connected with the outlet'port and the motor ports are blocked, a raise position in which one motor port is connected with the inlet port and the other motor port is connected with the outlet port, a lower position in which the connections between the motor ports and the inlet and outlet ports are reversed, and a float position in which all of the ports are interconnected.

These directional control valves are quite large and massive in many high pressure and large capacity hydraulic installations (as for example in the earth moving equipment field). Hence considerable force is required to shift the plunger between its various positions with the result that accurate positioning of the plunger is rendered difficult.

The object of the present invention is to provide a lowpressure remote control system for accurately shifting the plunger of a directional control valve between its operating positions. According to the present invention, a double acting piston motor is connected with the plunger and is operable by fluid from a low pressure source in accordance with the operation of a remote control valve connected between the source and the motor. The remote control valve includes a control member which is manually movable to vary in reverse senses the pressures in the working chambers of the double-acting motor to effect movement of the plunger. When the remote control valve is in a neutral position, the pressures in the working chambers are equal and the motor piston is positioned in the neutral position by a centering spring. When the control valve is moved in a first direction from the neutral position, the motor piston is moved toward the raise position against the opposing force developed by the centering spring, and when the control valve is moved in an opposite second direction, the motor piston is moved in the opposite direction toward the lower position against the opposing force developed 'by the centering spring. When the control valve is moved further in the second direction, the motor piston is moved toward the float position against the opposing forces developed both by the centering spring and by additional spring means which are operable only when the motor piston is shifted on the other side of the lower position from the neutraf position.

The valve embodying the invention includes fluid-pressure responsive feel means which provides an indication to the operator of at least one of the positions toward which the control valve (and, consequently, .the valve plunger) is being moved. The pressure-responsive means includes a feel motor of the piston type associated with the control valve and having a working chamber con- ,of the control valve toward its float position.

Patented Oct. 8, 1963 "Ice nected with one of the working chambers of the plunger actuating motor to develop a force resisting movement embodiment of the invention the feel device is operable throughout the entire travel of the control valve in the second direction referred to above, and means are provided for presenting a sharp deviation'in the feelsensed by the operator as the control valve is moved beyond its lower position toward the float position. In this embodiment, movement of the control valve from its neutral position toward the raise position is resisted by spring means the compression of which is sensed by the operator.

In the preferred embodiment of the invention, the control valve is continuously biased towand the neutral position, by a' centering spring and the feel device is operable only when the control valve is moved beyond the lower position toward the float position. In this embodiment the operator senses the compression of the centering spring as the control valve is moved from neut-r-al toward the raise or lower positions, and during movement of the control valve from the lower to float position, the opposing force developed by the pressureresponsive feel device as'well as the compression of the centering spring is felt. Thus the operator receives an indication when the control valve element approaches the float position.

Other advantages of the invention will become apparent from a study of the following specification when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram partly in section showing the hydraulic system;

FIG. 2 is a section-a1 view of the remote control valve takenalong line 2.2 of FIG. 3;

FIG. 3 is an axial sectional view of the remote control valve;

FIG. 4 is an axial sectional view of the actuating motor means for positioning the plunger of the directional control valve; and

FIG. 5 is a detailed sectional View of another embodiment of the hydraulic feel device illustrated in FIG. 3.

Referring to FIG. 1, a remote control valve 11 is provided for controlling a motor-actuated four-position hollow-plunger directional control valve 12. The directional control valve includes a housing 13 having inlet and outlet ports 14 and 15, respectively, and a pair of motor ports, not shown. Extending through the housing is a bore 16 encircled by longitudinally-spaced annular grooves 17, 18, 19, 21 and 22. Grooves 18 and 21 communicate with inlet port 14 via chamber 23 and groove 19 communicateswith outlet port 15 via chamber 24.

bore 37. A conventional springebiased check valve as-.

sembly, not shown, is mounted in bore 37 for preventing back flow from passages 43.

A positioning motor 45 is provided for moving the plunger 27 between conventional raise, neutral, lower and float positions illustrated by the letters R, N, L and F in FIG. 1. Inlet port 14 is connected with a first source of pressure fluid P of fairly large capacity (for example, g.p.m.), tand'outletport 15 is con- In one nected with sump. The motor grooves 17 and 21 are connected with the working chambers of hydraulic motor M via the conduit connections schematically illustrated by the broken lines in FIG. 1'. When plunger 27 is in the neutral position, the inlet and outlet ports 14 and 15 are interconnected via chambers 23, valve grooves 29 and 31, housing groove 19, and chamber 24. Fluid flow to and from motor grooves 17 and 22 is blocked by lands 3-3 :and 35, respectively, with the result that the piston of motor M is held stationary. When plunger 27 is moved to the left to the raise position, pressure fluid is transmitted from port 14 to motor groove 22 via chamber 23, groove 21, passages 42, bore 37 and passages 43, and motor groove 17 is connected with sump via passages 39, bore 36, and one path including passages '38 and chamber 24, and another path including passages 41, chamber 19 and chamber 24. The piston of motor M will move upward. When plunger 27 is moved to the right to the lower position, pressure fluid is supplied to motor groove '17 via port 14, chamber 23, passages 41, bore 36 and passages 39, and motor groove 22 is connected with sump via passages 42, bore 35, passages 43, chamber 24 and port 15, whereupon the plunger of motor M moves downward. When the valve plunger is moved further to the right to the float position, ports 14 and 15 and motor grooves 17 land 22 are all interconnected, since chamber 23 communicates with chamber 24 via grooves 29 and 19, since chamber 23 communicates with groove '17 via passages 39 and 41, bore as and passages 38, and since chamber v24 communicates 'with groove 22 via passages 43, bore 37 and passages 42.

Referring now to FIG. 4, the positioning motor 45 includes a first cylindrical housing 46 connected with housing 13 by means, not shown. Housing 46 has, on its inner surface, an annular groove 47 and a stop 48. A second cylindrical housing 49 having an annular flange 51 is mounted for limited sliding movement in housing 46 between stop 48 and snap ring 52 mounted in groove 47. Housing 49 has a bore 53 which receives a looselyfitted movable cylinder 54 rigidly connected with valve plunger 27 by screw-thread connection 55. Cylinder 54 is slidably movable on a stationary guide piston 56 which is rigidly connected with housing 49 by a pair of coaxial, radially-spaced tubular piston rods 57 and 58. Cylinder 54 and piston 56 constitute a hydraulic actuating motor having opposed working chambers 59 and 61. Working chamber 59 communicates with port 62 in housing 49 via bore 63 in hollow piston rod 57, radial passages 64 and chamber 65, and Working chamber 61 communicates with housing port 66 via radial passages 67, annular passage 63 defined between the coaxial piston rods, radial passages 69 and chamber 71.

Cylinder 54 is provided on its inner periphery with a pair of longitudinally-spaced grooves in which are mounted snap rings 72 and 73. A pair of coaxial compression springs 74 and 75 encircle rod 57 and react between an annular seal 76 and a movable washer 77 and urge them in opposite directions into engagement with snap rings 72 and 73, respectively. The inner diameter of snap ring 73 is greater than the outer diameter of the axial projection 56a of piston 56 so that when plunger 27 is displaced to the right to the lower position, the outer end of projection 56a engages washer 77. Further displacement of the plunger to the right toward float position is resisted by springs 74 and '75 as will be described in greater detail below. On its outer periphery,

' cylinder 54 is provided with a groove in which is mounted snap ring 78. A pair of axially aligned, longitudinallyspaced sleeves 79 and 8-1 are arranged within housing 46 and are provided at their adjacent ends with in-turned flanges 82 and 83 which engage ring 78 and plunger shoulder -85, respectively. Centering spring -86 reacts between the out-turned flanges on the opposite ends of sleeves 79 and 81 to bias plunger 27 toward-the neutral position.

Referring now to FIG. 3, the remote control valve 11 includes a housing 1131 having inlet and outlet ports 1112 and 1113, respectively, and a bore 104 encircled by iongitudinally spaced grooves 1135 through 169. Grooves 1115 and 10 9 communicate with each other and with inlet port 162 via passage 111. Groove 107 communicates with port 103 via passage 112. Motor grooves 1116 and 163 communicate (via passage means, not shown) with the motor ports 113 and 14, respectively, shown in PEG. 1. These motor ports are connected, respectively, with ports 62 and 66 of the plunger positioning motor 45 by conduits 115 and 116, respectively. Consequently, groove 1116 and chamber 59, and groove 1118 and chamber 61, respectively, are in constant communication. As shown in FIG. 2, a relief valve 111? relieves excessive pressure in the fluid passage 111 to the passage 112.

Sliclably mounted in bore 104 is a valve plunger 117 provided with longitudinally-spaced grooves 118 and 119 defined by lands 121, 122, and 123. First and second orifice grooves 124 and 125 are formed in the surface of land 122 and extend longitudinally from opposite ends of the land partway toward the other end.

A positioning detent and hydraulic feel device 126 for plunger 117 is provided and includes a cylindrical housing 127 connected with housing 101 by means (not shown). The left-hand end of valve plunger 117 extends into housing 127' and is provided with an enlarged cylindrical portion 128. The plunger contains an axial bore 129 that extends inward from the left-hand end of the plunger and terminates in radial passages 131 in groove 118. Cylindrical portion 123 is counterbored to define cylinder 132 in which hydraulic feel piston 133 is slid ably mounted. Piston 133 has a rigid axial projection 134. The travel of piston 133 to the left in cylinder 132 is limited by snap ring 13201. On its inner surface, housing 127 is provided with a groove in which is mounted snap ring 136. Coaxially arranged about plunger portion 128 is a sleeve 135 provided at one end with an in-turned flange which engages plunger shoulder 137. Spring 138 reacts between housing 101 and out-turned flange 139' on sleeve 135 to urge plunger 117 to the left, and when flange 139 engages ring 136, plunger 117 is in the neutralestablishing position illustrated in FIGS. 1 and 3.

A pair of annular detent collars 141 and 142 are mounted coaxially on plunger portion 128 and are provided on their adjacent ends with chamfered surfaces between which is arranged a ring of balls 14.3. Slida-bly mounted in the left-hand end of housing 127 is an end seal plate 144. Spring 145 reacts between the seal plate and collar 141 to urge the plate to the left against snap ring 146 (mounted in a groove on the inner periphery of housing 127) and to urge the collar and ball assemblage to the right against snap ring 135, whereby balls 143 are urged radially inward into contact with the outer periphery of plunger portion 128. It is important to note that in the FIG. 3 embodiment, the free end of projection 134 engages plate 144 when plunger 117 is in the illustrated neutral position. As will be described below, plunger 117 is axially shiftable in its housing between float, lower, neutral and raise positions by means of the pivotally mounted operating lever 147 (FIG. 1). When the lever is moved counterclockwise to the position indicated by the letter F, plunger 117 is shifted to the left to a float position in which groove 148 in the outer periphery of plunger portion 128 re ceives detent balls 143 to lock the plunger. Passage 149 afliord-s communication between passage 112 and the interior of housing 127.

Operation In operation, the outlet port 1113 of remote control valve 11 is connected with sump and inlet port 1112 is connected with a second source P of relatively small capacity (for example, 3 gpm.) compared with that of source P With operating lever 147 in the neutralestablishing position shown in FIG. 1, a first fluid path from source P to sump is established via port 102, passage 111, groove 119, orifice groove i125, groove 107, passage 1-12 and port 103. Owing to the back pressure developed by the restricted orifice defined by groove 125 and bore 104, fluid flows also from groove 119 to working chamber 61 of the positioning motor 45 via groove 198, port 1 14, conduit 116, port 66, chamber 71, and passages 69, 68, and 67. Similarly, a second fluid path from source P to sump is established via port 102, passage 111, grooves 118, 124, and 107, passage 112 and port 1115. Owing to the back pressure developed by the restricted orifice defined by groove 124 and bore 104-, fluid flows also from groove .118 to working chamber 59 via groove 196, port 1113, conduit 115, port 52, passages 64, and bore 63. Chambers 61 and 59 contain fluid under equal pressure and consequently plunger 27 is maintained in its neutral position by centering spring 86. At this point it should be mentioned that even though motor 45 is of the differential area piston type, the pressure of the fluid in chambers 59 and 6 1 is relatively low and the forces acting on the effective end surfaces of the piston are not suflicient to move the cylinder against the biasing force of the centering spring. Further-more, if desired, the porting of lands 121 and 123 or the relative dimensions of grooves 124 and 125 may be designed to compensate for the unequal effective working surfaces of the differential area piston. Fluid at the neutral idling pressure is fed to chamber 132 of the hydraulic feel device via port 102, passage 111, passages 13 1, and bore 129 with the result that piston 133 is urged to the left against ring 132a and the free end of piston projection 134 contacts plate 144. Spring 138 is preloaded to develop a force equal to the force developed by the fluid at idling pressure in chamber 132 so that plunger 117 is held in the center position. The rate of the spring is also matched to the p.s.i. rate of the orifice length so that the operator senses the same handle feel as handle 14-7 is pivoted toward the raise or lower positions.

Assuming that it is desired to displace plunger 27 to the left to the raise position, lever 147 is pivoted in the clockwise direction and plunger 117 is shifted to the right toward its raise position against the opposing force developed by spring 138. As plunger .117 is shifted to the right, the lengths of orifices 125 and 124 progressively increase and decrease, respectively, with the result that the back pressure in groove 108 and chamber 51 progressively increases and the back pressure in groove 1116 and chambers 59 and 132 progressively decreases. The pressure differential between chambers 51 and applies a force on cylinder 54 tending to move plunger 27 to the left against the force developed by spring 86. When plunger 1117 reaches the raise position, motor groove 1% is isolated from source P by land 121, but remains in communication with sump (via grooves 118, 124 and 167, passage 112, and port 1%) to afford stability to the system. Since chambers 132 and Share in communication With motor groove 1%, these chambers are also vented. Owing to the increase in length of orifice groove 125, the back pressure in working chamber 61 is quite high with the result that plunger 27 is shifted fully to the left (against stationary piston 56) to the raise position.

Upon release of lever 147, spring 1 38 reacts to return plunger 117 to its neutral-establishing position to effect equalization of pressure in working chambers 59' and 61 as described above, whereupon plunger 27 is returned to its neutral position by spring 86. The pressure in chamber 132 again increases to idling pressure, and piston 13 3 is urged to the left until projection 134 again abuts end plate 144.

In order to shift plunger 27 to the right to its lower position, lever 147 is pivoted in the counterclockwise direction to shift plunger 117 to the left toward its lower position. Since piston extension 134 is in engagement with end plate 144 and since chamber 132 contains fluid at idling pressure, movement of plunger 117 to the left is opposed by the forces developed by the fluid in chamber 132 which resist movement of cylinder 128 to the left relative to stationary piston 133. Owing to the progressively increasing back pressure which results from the increasing length of orifice groove 124 during movement of plunger 117 to the left, the back pressure in chamber 132 progressively increases to provide a hydraulic feel which is sensed by the operator. Furthermore, since the lengths of orifice grooves 124 and 125 are progressively increased and decreased, respectively, the back pressures in working chambers 59 and 61 progressively increase and decrease, respectively, to apply on cylinder 54a force tending to move plunger 27 to the right against the force developed by spring 86. When plunger 11'? reaches the lower-establishing position, land 123- isolates motor groove 108 from the source P said motor groove remaining in communication with sump via grooves 119 and 125, chamber 1111, passage 1-12 and port 103. As a result of the increased length of orifice groove 124-, the back pressure in groove 106 and chambers 59 and .132 is relatively high, and since chamber 61 is vented, plunge-r 27 is shifted to the right against the force of spring to the lower position.

Owing to the increased pressure in chamber 132, the operator senses a relatively strong force opposing further movement of lever 147 in the counterclockwise direction. Since piston extension 56a engages washer 77 when plunger 27 is in the lower position, further movement of cylinder 54 and plunger 27 to the right will be opposed by springs 86, 74 and 75 in the event that plunger 11'? should overshoot its lower-establishing position.

As lever 14-7 is pivoted further to the left toward the float-establishing position, the length of orifice groove 124 increases further and the back pressure in groove 1% and chambers 59 and 132 increases correspondingly. Owing to the increase in pressure in chamber 132, the operator senses a progressively increasing opposing force during this movement of the lever in the counterclockwisedirection. This is desirable to prevent the operator from unintentionally causing plunger 27 to be moved to the float position. Furthermore, owing to the relatively strong force developed by springs '86, 74 and 75 resisting movement of plunger 27 to the float position, a considerably higher pressure differential between chambers 59 and 61 is required to move plunger 27 to the right from its lower position. This pressure differential is reflected in the increased pressure force in chamber 132 resisting movement of lever 14-7 in the counterclockwise direction. As plunger 117 is further displaced to the left toward its float-establishing position, land 122 interrupts communication between motor. groove 1% and sump, and the pressure in groove 1% and chambers 59 and 132 rises sharply to a maximum value determined by the setting of relief valve 110. The operator senses this sharp pressure rise in chamber 132 and realizes that plunger 117 has now reached the float-establishing position. The pressure differential in chambers 55 and 6 1 is now of such magnitude as to shift plunger 27 rapidly to the right to the float position against the counteracting forces developed by springs 86, 7d and 75, and plunger 117 is locked in the floatestablishing position by engagement of detent balls 143 in groove 1148.

Upon the application of a sufficient clockwise movement on lever 1'47, detent balls 143 are urged radially out of groove 148 to release plunger .117 from the floatestablishing position. Plunger 117 is biased toward its neutral-establishing position by the pressure force in chamber 132 which forces cylinder 12% to the right relative to piston 133 and end plate 144.

In the hydraulic feel embodiment of FIG. 3, the remote control plunger 117 is spring centered in one direction and pressure centered in the other direction. In the preferred embodiment illustrated in FIG. 5, the remote control plunger 117 is spring centered in both directions and the hydraulic feel device is operable only when the plunger is displaced to the left beyond the lower-establishing position. Referring to FIG. 5, a sleeve 2% is arranged coaxially on plunger 117' and is provided at one end with an in-turned flange 292 which engages split ring 263 mounted in a groove in the outer periphery of the plunger. The coaxially-arranged centering spring 138 reacts between the out-turned flange of sleeve 201 and flange 139' of sleeve 135' to position plunger 117 in the neutral position. It is important to note that in the neutral position, the piston 133' is biased against split ring 13241 by the idling pressure fluid in chamber 132; and the free end of projection 134' is spaced from end plate 144'.

In operation, movement of lever 147 in the clockwise direction causes plunger 117 to be shifted to the right to the raise position against the counter-acting force developed by spring 138. Owing to the progressive compression of spring 138', the operator senses the same feel when lever 147 is pivoted in the clockwise direction from neutral as is sensed in the FIG. 3 embodiment. Upon release of lever 147, spring 138 expands to return plunger 117 to its neutral position,

Movement of lever 147 in the counter-clockwise direction causes plunger 117' to be shifted to the left to the lower position against the counter-acting force developed by the compression of spring 138'. Consequently, in the FIG. 5 embodiment, the operator senses the same feel (resulting from the compression of centering spring 138) when the lever 147 is pivoted to the lower-establishing position as is sensed when the lever is pivoted to the raise-establishing position.

When plunger 117' is in the lower position, the back pressure in chamber 132 is relatively high (owing to the increased length of orifice groove 12.4) and piston 133 is urged to the left to cause projection 134 to engage end plate 144. As lever M7 is pivoted further in the clockwise direction, plunger 117 is shifted to the left toward the float-establishing position against both the force developed by spring 138' and the force developed by the fluid in chamber 132' resisting movement of cylinder 12% to the left relative to stationary piston 133'. Since the back pressure in chamber 132 progressively increases as the length of orifice groove 124 is increased, the operator sense-s an additional progressivelyincreasing opposing force as lever 147 is pivoted toward the fioat-establishing position, which force is considerably greater than that which is experienced when lever 147 is pivoted to either the raise or lower-establishing position. When the sump connection of motor chamber 106 is closed by land 122, the pressure in chamber 132' increases sharply to a maximum value to present an indication to the operator that the plunger is in its floatestablishing position.

Locking and release of plunger 117 in the float position by the detent balls 143 is accomplished in the same manner as described above with reference to the PEG. 3 embodiment.

While the best forms and embodiments of the invention known to applicants have been illustrated and described, it will be apparent to those skilled in the art that other changes and modifications may be made in the apparatus described without deviating from the scope of the invention as set forth in the following claims.

We claim:

1. A remote control system comprising a. a fluid pressure operated motor having a stationary element, a working chamber and a movable element responsive to the pressure in the working chamber and movable between first and second positions;

b. first spring means continuously resisting movement of said movable element toward the first position;

0. second spring means arranged to resist'movement of said movable element toward the first position only after that element has moved a predetermined distance away from the second position;

d. a source of fluid under pressure;

0. a pressure graduating valve connected with the source and the working chamber and having a housing and a valve member movable in opposite directions from an intermediate position toward first and second positions to increase and decrease, respectively, the pressure in the working chamber; and

1. means responsive to the pressure in the working chamber for developing a force that resists movement or" the valve member toward its first position during at least a terminal portion of such movement.

2. The remote control system defined in claim 1 in which the pressure responsive means comprises a. a second fluid pressure motor carried by said valve member and having a working chamber and two relatively movable motor elements, one of said motor elements being arranged to abut a part of said housing during at least said terminal portion of such movement; and

b. passage means interconnecting the Workin g chambers of the two fluid pressure motors. A remote control system comprising a. a controlled member movable between first and second positions on opposite sides of a neutral position;

b. first and second fluid pressure motor chambers, each chamber having a movable reaction surface, the

movable reaction surfaces being connected with the controlled member in opposing relation, the reaction surface of the first motor chamber being arranged to-move the controlled member toward the first position;

0. centering spring means continuously biasing the controlled member toward said neutral position;

d. second spring means arranged to resist movement of the controlled member toward the first position only after that member has moved a predetermined distance away i-rorn the neutral position in the direction of the first position;

e. a source of fluid under pressure;

1. a pressure graduating valve connected with the source and the first and second motor chambers and having a housing and a movable valve member, the movable valve member being shiftable in opposite directions from a neutral position toward first and second positions to graduate in reverse senses the pressures in the two motor chambers, movement toward the first position producing increasing and decreasing pressures in the first and second motor chambers, respectively, and movement toward the second position producing increasing and decreasing pressures in the second and first motor chambers, respectively; and

g. means responsive to the pressure in the first motor chamber for developing a force that resists movement of the movable valve member toward the first position during at least the terminal portion of the movement of that member from the neutral position toward the first position.

4. The remote control system defined in claim 3 a. in which the pressure responsive means is effective to resist movement of the movable valve member toward its first position throughout movement of that member from its neutral position to its first-position; and

b. including spring means continuously reflective to resist movement of the movable valve member from its neutral position toward its second position.

5. The remote control system defined in claim 4 in which the pressure responsive means comprises a. a fluid pressure feel motor carried by said movable valve member and having a working chamber and two relatively movable motor elements, one of said motor elements being arranged to abut a part of said housing continuously during movement of said valve member between its neutral position and its first position; and

1b. passage means connecting the working chamber of the feel motor with the first motor chamber.

6. The remote control system defined in claim 3 a. in which the pressure responsive means is eifective to resist movement of the movable valve member toward its first position only during said terminal portion of such movement; and I b. including second centering spring means biasing the movable valve member toward its neutral position.

7. The remote control system idefined in claim 6 in which the pressure responsive means comprises a. a fluid pressure teel motor carried by said movable valve member and having a working chamber and two relatively movable motor elements, one of said motor elements being arranged to abut a part of said housing only during said terminal portion of movement; and

b. passage means connecting the working chamber of the feel motor with the first motor chamber.

8. The remote control system defined in claim 3 in which the pressure responsive means comprises a. a fluid pressure feel motor carried by said movable valve member and having a working chamber and two relatively movable motor elements, one of said elements being arranged to abut a part of said housing during at least said terminal portion of movement; and

b. passage means connecting the working chamber of the feel motor with the first motor chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,901,910 Johnson et a1 Mar. 21', 1933 2,608,263 Garrison Aug. 26, 1952 2,762,342 Adams et a1. Sept. 11, 1956 2,975,762 Blatt et a1 Mar. 21, 1961 

1. A REMOTE CONTROL SYSTEM COMPRISING A. A FLUID PRESSURE OPERATED MOTOR HAVING A STATIONARY ELEMENT, A WORKING CHAMBER AND A MOVABLE ELEMENT RESPONSIVE TO THE PRESSURE IN THE WORKING CHAMBER AND MOVABLE BETWEEN FIRST AND SECOND POSITIONS; B. FIRST MEANS CONTINUOUSLY RESISTING MOVEMENT OF SAID MOVABLE ELEMENT TOWARD THE FIRST POSITION; C. SECOND SPRING MEANS ARRANGED TO RESIST MOVEMENT OF SAID MOVABLE ELEMENT TOWARD THE FIRST POSITION ONLY AFTER THAT ELEMENT HAS MOVED A PREDETERMINED DISTANCE AWAY FROM THE SECOND POSITION; D. A SOURCE OF FLUID UNDER PRESSURE; E. A PRESSURE GRADUATING VALVE CONNECTED WITH THE SOURCE AND THE WORKING CHAMBER AND HAVING A HOUSING AND A VALVE MEMBER MOVABLE IN OPPOSITE DIRECTIONS FROM AN INTERMEDIATE POSITION TOWARD FIRST AND SECOND POSI- 